Field of the Invention
The invention relates to a method of starting up a printing machine after washing a rubber blanket thereof.
The rubber blanket is used to transfer ink from a plate cylinder, whereon a printing plate is mounted, to a printing material, which runs through a nip between the blanket cylinder and an impression cylinder. During a production printing run, a given quantity of ink is always present on the blanket cylinder, and this quantity is refilled by the plate cylinder to the extent to which it is transferred to the printing material. When the printing machine is started up after the rubber blanket has been washed, this layer of ink is missing. Therefore, at the beginning of the start-up, the rubber blanket removes a quantity of ink from the plate cylinder which is significantly greater than that during the production printing run; the layer produced on the rubber blanket, consequently, is thin when compared with production printing, however, and the resulting imprint on the printing material is weak. Therefore, every time a printing machine is started up after the rubber blanket has been washed, a start-up phase of some ten sheets duration is necessary in order to achieve the production printing state. Within this start-up phase, waste sheets or rejects are printed.
It is accordingly an object of the invention to provide a method of starting up a printing machine which permits the start-up phase to be shortened, and the quantity of rejects or waste to be reduced.
With the foregoing and other objects in view, there is provided, in accordance with the invention, a method of starting up a printing machine after washing a rubber blanket thereof, which comprises pre-inking the rubber blanket by performing at least one complete revolution of the rubber blanket in contact with the inked printing plate before the start of printing.
In accordance with another mode, the method invention includes performing a plurality of complete revolutions, between 4 and 20 thereof, of the rubber blanket.
In accordance with a further mode, the method invention includes, before the start of printing, feeding a given quantity of ink into the inking unit of the printing machine, in order to compensate for the loss of ink in the inking unit resulting from pre-inking the rubber blanket.
In accordance with an added mode of the method invention, the given quantity of ink at least approximately corresponds to the quantity of ink on the rubber blanket under production printing conditions.
In accordance with an additional mode, the method invention includes concluding the feeding in of the given quantity of ink by starting up the printing operation.
In accordance with a concomitant mode, the method invention includes feeding in an excess quantity of ink during the printing of the first printed sheet.
Thus, the method according to the invention calls for the rubber blanket to be pre-inked, by performing at least one complete revolution in contact with the inked printing plate, in a prior phase before the start of printing.
In order to compensate for the loss of ink in the inking unit caused by the pre-inking, a given quantity of ink is previously fed into the inking unit, preferably before the start of printing. This quantity of ink corresponds in substance to the quantity of ink which would be found on the rubber blanket under production printing conditions.
The action of feeding in the quantity of ink can be begun before or after the beginning of pre-inking. In order to have a good ink gradient in the printing unit, as similar as possible to production printing, at the beginning of printing, the flow of ink fed in during the prior phase is preferably metered so that as the printing operation starts, the given quantity of ink is just being fed in.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a method of starting up a printing machine, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.